1. Field of the Invention
The present invention relates to a method for X-ray micro-diffraction measurement in which diffracted X-rays occurred at a minute portion of a specimen upon irradiating the minute portion with X-rays. Also, The present invention relates to an apparatus for performing the same method.
2. Description of the Related Art
In the X-ray measurement in which a specimen containing a large number of crystal grains, that is, a polycrystal specimen, is irradiated with X-rays having large cross sectional beam diameter, a large number of crystal grains exist in an area which is to be irradiated by the X-rays. Therefore, a large number of crystal grains in that area comes to satisfy the diffraction condition, so that a large number of crystal grains can direct diffracted X-rays to an X-ray detector arranged in a predetermined position relative to the specimen. In this case, it is possible to detect diffracted X-rays by the X-ray detector arranged in a fixed position.
However, there may be a case where it is necessary to know a diffracted X-ray information for a minute sample or a minute area of a polycrystal specimen, which may be not more than 100 .mu.m in diameter. In such case, an irradiation field of X-rays becomes narrow, so that the number of crystal grains contained in such narrow area becomes small. Therefore, regardless of crystal grains at which the X-ray diffraction occur, detection of diffracted X-rays by an X-ray detector arranged in a fixed position becomes impossible frequently.
Further, there may be a case where only one crystal grain exists in the field of X-ray irradiation, that is, a case of single crystal, in which diffraction of X-rays occurs at a specific diffraction angle. In a case where a few crystal grains exist within the X-ray irradiation field, including the case of the single crystal condition, Debye ring formed by diffracted X-rays may not be found unless a sample is swung.
An X-ray micro-diffraction apparatus, which makes an X-ray diffraction measurement for a minute portion of a specimen possible, includes rotary systems rotatable about at least independent two axes, which are usually called as a .chi. axis and a .phi. axis, respectively, and cross with each other at an irradiation point of X-rays. A specimen is supported by those rotary systems and is rotated about the orthogonal two axes independently by the rotary systems during the minute portion thereof is irradiated with X-rays.
Such independent rotations of the specimen about the two axes disorders directional distribution of crystal lattice planes of crystal grains with respect to the incident X-rays. As a result, X-rays diffracted by these crystal grains can be detected by the X-ray detector arranged in a constant position even if there is few crystal grains exist in an irradiation area of X-rays of the specimen.
The X-ray micro-diffraction apparatus for detecting diffracted X-rays from the minute portion of the specimen can be constructed as shown in, for example, FIG. 3. In FIG. 3, the .chi. axis is set coincident with an optical axis X0 of X-rays `R ` and a .phi. rotary device 51 is arranged on the .phi. axis line. The .phi. rotary device 51 rotates a .phi. arm 52 about the .phi. axis. The .phi. arm 52 supports an .omega. rotary device 53 which rotates an .omega. arm 54 about the .omega. axis which is orthogonal to the .chi. axis, that is, the optical axis X0 of X-rays `R`.
The .omega. arm 54 supports a .phi. rotary device 56 which rotates the specimen `S ` about the .phi. axis so as to rotate in a plane. The .phi. axis is contained in a plane which contains the X-ray optical axis XO and is orthogonal to the .omega. axis, and also passes through a cross point of the .omega. axis and the .chi. axis. The specimen `S ` is arranged at the cross point of the .chi. axis, the .omega. axis and the .phi. axis, to thereby be located on an irradiation point of X-rays `R`.
A curved PSPC, namely, a position sensitive proportional counter 57 is arranged as the X-ray detector in a position remote from the specimen `S`, by an appropriate distance. The PSPC 57 detects a time difference between pulses generated at opposite ends of a core line of a PC, namely, a proportional counter so that a position resolution can be obtained in a direction of the core line of the PC, that is, in a linear line. In FIG. 3, the position resolution is given in the linear direction within a plane orthogonal to the .omega. axis, so that X-rays having different diffraction angles are detected simultaneously along the linear direction.
In the X-ray micro-diffraction apparatus mentioned above, the specimen `s ` is rotated about the .chi. axis and the .phi. axis independently, so that an arbitrary minute portion of the specimen `S ` can be brought to the irradiation point of X-rays `R`. Therefore, the PSPC 57 can detect all of X-rays diffracted at the specimen `S`.
The specimen `S ` is rotated about the .omega. axis in order to regulate the incident angle of X-rays to the specimen `S`. After the incident angle is set to a predetermined value, for example, 20.degree. to 30.degree., the specimen `S` is fixed in the position around the .omega. axis.
In the device shown in FIG. 3, the .chi. axis is set coincident with the optical axis X0 of X-rays and the .omega. axis rotary system is mounted on the .omega. axis rotary system. However, the X-ray micro-diffraction apparatus may have another construction such as shown in FIG. 4, in which the .chi. axis rotary system is mounted on the .omega. axis rotary system so that the .chi. axis is not always coincident with the optical axis X0 of X-rays.
In any way, the conventional X-ray micro-diffraction apparatus for a minute portion of a specimen requires at least two rotary systems, namely, the .chi. axis rotary system and the .phi. axis rotary system, resulting in a complicated construction.
Further, when the cross point of these two axes is not exactly defined to thereby cause a crossing error between these two axes, the irradiation field of X-rays on the specimen `S ` is broadened, causing the measurement of diffracted X-rays at a minute portion of the specimen to be meaningless. Therefore, the positional relation between these two axes must be severely regulated. However, such precise regulation of the positional relation has been very difficult.
Further, since the PSPC 57 is a one-dimensional detector, it is necessary to rotate the specimen `S ` about the .chi. axis in order to detect X-rays diffracted by the specimen `S`, causing a time required for the X-ray diffraction measurement to be long.